Ceramic is conventionally known as a piezoelectric material. However, ceramic has drawbacks in that it is brittle and, if fabricated thin, it is easy to break. Since, as a practical matter, ceramic can not be made into thin films, a bimorph (a two layered element) made of a ceramic achieves only a small amount of bending upon the application of an electric field thereto. Recently, a thin polymer piezoelectric material has been employed in making a cartridge of a microphone, a speaker and a headphone. A bimorph element comprising films made of a mixture of PVF.sub.2 (polyvinylidene fluoride) and PZT powder was reported by J. Ohga in a report presented to the Meeting of Technical Group on Electro Acoustics, and published in Sept. 27, 1972 by the Institute of Electronics and Communication Engineer of Japan. However, in the report the films were not stretched before a fabrication of the bimorph, therefore, the bimorph could not utilize the piezoelectric characteristics of PVF.sub.2. Further, the bimorph including PZT powder had a thickness of 2.5 mm and was not made thinner.
Various prior art devices exist for controlling light. There are display devices in which a number of electric light bulbs are arranged, and the controlled on and off operation thereof is utilized. Such a display device consumes a large amount of power and is expensive to construct. Display devices utilizing controlled electron collision against a phosphor material or using a liquid crystal element can not be manufactured inexpensively on a large scale. Also known is a shutter device using a ceramic piezoelectric element. But such a device can not achieve an effective shutter function due to the relatively small amount of bending of the bimorph comprising the ceramic piezoelectric element, thus resulting in only a limited amount of light control.